On Feb 4, 2016 5:58 AM, "Ard Biesheuvel" <ard.biesheuvel@xxxxxxxxxx> wrote: > > OK, since Sai has confirmed that Windows leaves interrupts enabled when > calling the EFI variable store related runtime services, we should be able > to do the same for Linux, or at least be slightly more confident that we > won't have to back out this change later. Could this use a mutex instead of a spinlock? Can someone with a mixed mode setup read a variable in a loop and make sure it doesn't crash and burn? It should work fine, but explicit testing would be nice. (It's interesting mainly because doing a mixed mode call with interrupts on can result in a non-IST CPL0 to CPL0 exception delivery, which won't result in a stack switch. This could easily trigger a stack overflow, logic bug, microcode bug, or as-yet-unknown CPU "feature". Hmm. We should also audit the mixed mode entry code to make sure that the high bits of RSP are explicitly clear before switching into compat mode. If I had to make a guess about how CPUs behave, I'd guess pessimistically: Intel CPUs clear the high bits of RSP when switching into long mode due to interrupt delivery, and AMD CPUs leave them set just to mess with us. Also, a WARN_ON(in_interrupt()) somewhere might be a good sanity check. --Andy -- To unsubscribe from this list: send the line "unsubscribe linux-efi" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
